This shell script prints the given number's sum of all digits, For eg. If no is 123 it's sum of all digit will be 1+2+3 = 6.
# Linux Shell Scripting Tutorial 1.05r3, Summer-2002
# Written by Vivek G. Gite <email@example.com>
# Latest version can be found at http://www.nixcraft.com/
# 1) Input number n
# 2) Set sum=0, sd=0
# 3) Find single digit in sd as n % 10 it will give (left most digit)
# 4) Construct sum no as sum=sum+sd
# 5) Decrment n by 1
# 6) Is n is greater than zero, if yes goto step 3, otherwise next step
# 7) Print sum
if [ $# -ne 1 ]
echo "Usage: $0 number"
echo " I will find sum of all digit for given number"
echo " For eg. $0 123, I will print 6 as sum of all digit (1+2+3)"
while [ $n -gt 0 ]
sd=`expr $n % 10`
sum=`expr $sum + $sd`
n=`expr $n / 10`
echo "Sum of digit for numner is $sum"